The “author and finisher” of the aircraft that fly us to our destinations is the company that built it, not us. So, it is with the new life we live out once we accept Jesus as our Lord and Savior. God builds it and His faithfulness is absolutely necessary to our getting to our ultimate destination in Heaven.
God is the Founder of our faith and the Source of our ability to overcome the evil in our lives. As He works in us to “work and will according to his good pleasure” we can reject legalism and, at the same time, surrender to the life Christ has obtained on our behalf.
In fact, that surrender is only made possible by His saving and sanctifying love, a love that is infinitely more desirable to experience than living in the misery of self-effort expended to gain a useless self-righteousness.
…let us run with endurance the race that is set before us, looking unto Jesus, the author and finisher of our faith, who for the joy that was set before Him endured the cross, despising the shame, and has sat down at the right hand of the throne of God. Hebrews 12:1-2 (NKJV)